Temperature enhanced field emission x-ray tube



April 1965 w. P. DYKE ETAL 3,179,832

TEMPERATURE ENHANCED FIELD EMISSION X-RAY TUBE Filed Jan. 12, 1960 INVEN TOR. WAL 77:7? P DYK E FRANK J GPUNDHAUSER Buckhorn, Cheafham 8B/ore ATTORNEYS 3,179,832 TEMPERATURE ENHANQED FIELD EMISSION X-RAY TUBEWalter P. Dyke and Frank J. Grundhauser, McMinnville, reg., assignors toField Emission Corporation, McMinnville, 0reg., a corporation of OregonFiled Jan. 12, 1960, Ser. No. 2,033

13 Claims. (Cl. 313-57) This invention relates to a temperature enhancedfield emission X-ray tube and more particularly to an X-ray tube adaptedfor pulse operation in which both thermal emission and field emission ofelectrons from a cathode structure are employed and in which an intensefocused stream of high velocity electrons is caused to strike an anodeduring a short period of time by applying a narrow square wave pulse ofhigh voltage across the anoded and cathode connections of the tube.

Tubes in accordance with the present invention have cathode and anodestructures which are capable of being employed to produce and impingeupon the anode an intense focused beam of electrons traveling at highvelocity to thereby produce high intensity X-rays. Electrons are emittedfrom the cathode by a combination of thermal and field emission and suchemission may be of the order of 2000 to 4000 amperes per squarecentimeter of emitting surface. Sufficient emitting surface may beprovided so that maximum currents, for example, of the order of 1000 to2000 amperes may be produced in such tubes. Such current is produced forvery short times, for example, times of the order of one-tenth totwo-tenths microseconds. The spacing the anodes and cathodes is suchthat the maximum voltage applied thereacross may be of the order of 300to 600 kv. and such that the tubes may have impedances of the'order of300 ohms. The maximum power applied to the tubes may therefore be of theorder of 300 to 1200 million watts so that an intense source of X-raysis provided for a short period of time during each operation of thetube.

In tubes in accordance with the present invention, electron-emission isfrom a plurality of cathode elements in the form of parallel heatedWires of small diameter supported in a cathode structure. The cathodestructure is constructed and positioned relative to an anode so that anelectron beam from the cathode elements is focused upon a target area onthe anode. In order to prevent undesired field emission of electronsfrom the supports for the cathode elements, such supports have theirsurfaces in the vicinity of the anode and directed toward the anode,carefully smoothed to avoid points or edges of small radius ofcurvature. Consistent repeated operation of such tubes requires thatsuch surfaces remain in a smooth condition.

tubes. In order to accomplish this, the supports for the cathodeelements can be heated to self-cleaning and smoothing temperatures byheating currents during such operation of the tubes. The leads for theheating currents for the cathode elements provide the supports for suchcathode elements and also provide electron beam focusing structureadjacent such cathode elements. Such leads are of a size relative to thewires forming the cathode elements that they are also heated to arelatively high temperature during operation of the tube. For example,in the case of tungsten cathode elements and leads, cathode elements maybe heated by a heating current to United States Patent 0 3,179,832Patented Apr. 20, 1965 ICE a temperature of 2900 to 3000 K. while theleads adjacent the emitting wires are heated to a temperature of theorder of 1900 to 2000 K. At such temperatures, any impurities upon thesurfaces of the leads are largely evaporated and the metal itself isself-smoothing by reason of surface migration of atoms thereon.

The voltage pulses applied between the anode and cathode of the tube arepreferably sufficiently short that the voltage is removed before ionsfrom the anode have reached the cathode structure to thus providetransit time isolation. Very little material is carried from the anodeto the cathode and, if the surfaces of the leads directed toward theanode are originally made very'smooth, the heating action referred toretains such smoothness.

The anode structure of the tubes preferably includes a thin plate formedto partially surround the cathode structrue so as to prevent strayelectrons from bypassing the anode and striking the tube envelope tothus damage the envelope or release contaminating gases therefrom. Suchanode may, however, be sufficiently thick that substantially all of theusable X-rays are emitted from the surface directed toward the cathode.In the preferred anode structure, the area of the anode which is struckby the electrons is positioned on an embossed portion extending out ofthe general plane of any portion of the anode to provide stiffeningridges around such area. Alternatively the anode may be of thin enoughfoil so that usable X-ray emission is produced-from the side of theanode opposite the cathode. Such foil anode may be semicircular shape incross section as to partly surround the cathode and may be supported sothat it also can be heated by passage of a heating current therethroughduring out gassing of the electrodes of the tube. In this connection thetube is carefully outgassed by extensive heating and pumping andaneffective getter is employed so that a vacuum of the order of 10* mm.of mercury is obtained. Also a glass for the envelope is selected whichis substantially impervious to all gases including helium, so that suchvacuum is maintained.

The anode and cathode structures of the present invention can becontained in tubes of relatively short length. When such tubes aresubjected to the high voltages referred to above, flash overs tend tooccur around the tube from the anode to the cathode connections. Inaccordance with the present invention, an anode connection has beendeveloped which effectively prevents such flash overs. Such connectionincludes a reentrant portion in an end of the envelope of the tube whichis filled with insulating material. The insulating material has a socketinto which the end of an insulating sheath of a solid dielectric coaxialcable can be inserted after the outer conductor of the cable has beenremoved from such end. This eliminates any air path between the anodeand cathode connections.

It is therefore an object of the present invention to provide animproved X-ray tube for pulse operation in which high currents can beproduced for short lengths of time by the application of short pulses ofhigh voltage so as to provide an intense X-ray output.

Another object of the invention is to provide an X-ray tube in whichfield emission enhanced by high temperature operation of a cathode ofsmall radius of curvature is employed to produce high intensity shortpulses of X-rays.

Another object of the invention is to provide a cathode structure for atemperature enhanced field emission X-ray tube in which a plurality ofelectron emitting elements of small diameter are heated to a thermalemission temperature by a heating current and are supported by leadswhich form part of an electron beam focusing structure and which arethemselves heated by such current to a cleaning and smoothingtemperature.

Another object of the invention is to provide a cathode structure for atemperature enhanced field emission X-ray tube in which the leads for aplurality of cathode elements supply heating current flowing throughsuch elements and also form part of an electron beam focusing structure.

Another object of the invention is to provide an improved anodeconnection particularly useful with X-ray tubes for preventing flashovers between the anode and cathode connections of such tubes when highvoltage pulses are applied between such connections.

A further object of the invention is to provide an improved structurefor connecting a solid dielectric coaxial cable to an electrode of atube in a manner which eliminates air paths for electric dischargesaround the envelope of the tube when high voltages are applied to suchtube.

Other objects and advantages of the invention will appear in thefollowing description of preferred embodiments shown in the attacheddrawing of which:

FIG. 1 is side elevation of an X-ray tube in accordance with the presentinvention with parts broken away to show internal structure;

FIG. 2 is a fragmentary end elevation on an enlarged scale of the anodeand cathode structures of the tube of FIG. 1, looking in the directionof the arrows 2-2 of FIG. 1;

FIG. 3 is a perspective view of the cathode structure of FIGS. 1 and 2on approximately the same scale as FIG. 2;

FIG. 4 is a perspective view of the anode structure of FIGS. 1 and 2 onapproximately the same scale as FIG. 2;

FIG. 5 is a view similar to FIG. 3 of a modified cathode structure;

FIG. 6 is a fragmentary side elevation of the cathode structure of FIG.5;

FIG. 7 is an end elevation of the cathode structure of FIG. 6, alsoshowing the upper end of a seal for the leads supporting such cathodestructure;

FIG. 8 is a perspective view similar to FIG. 4, showing modified anodestructure and a detail of the connection of such anode to a supportinglead;

FIG. 8a is a fragmentary perspective view showing a detail of thestructure of FIG. 8 on an enlarged scale;

FIG. 9 is a fragmentary horizontally cross section of the upper portionof the anode connection for the tube of FIG. 1 taken on the line 9-9 ofFIG. 1;

FIG. 10 is a view similar to FIG. 9 taken on the line '1010 of FIG. 1;

FIG. 11 is a View similar to FIG. 10 taken on the line 1111 of FIG. 1and showing a getter and shield structure for the anode seal; and

FIG. 12 is a vertical section of a getter and shield structure of FIG.11 taken on the line 1212 of FIG. 11.

Referring more particularly to the drawings, the X-ray tube of FIG. 1includes a glass envelope of any suitable form, for example, thecylindrical form shown, having an evacuated interior. An anode structure22 positioned in such envelope includes a trough-shaped anode 24 of thinsheet metal and a pair of supporting leads 25. The leads 26 pass througha press seal 27 forming part of a reentrant glass seal structure 28 atthe anode end of the tube. A cathode structure 30 also positioned in theenvelope 20 includes supporting leads 32 for an electron emittingportion of the cathode in the form of a plurality of parallel filamentwires 31 extending between the leads. The leads 32 are connected tolarger supporting leads 34 which pass through and are supported byanother press seal 35 forming part of a reentrant glass seal structure36 at the cathode end of the tube. The tube also contains a shield 38for the seal structure 36, which shield is supported from one of theleads 34 by a member 40.

The leads 32 extend through apertures 39 in the shield 38 so as to beout of contact with such shield. The tube also contains a shield 42 forthe seal structure 28, the shield 42 being supported from one of theleads 26 by a support member 44 which also forms one terminal for agetter heater 46.

The anode 24 of the anode structure 22 of FIGS. 1, 2 and 4 is ofrectangular trough-shape conformation and has its side portions 48secured to the anode supporting leads 26 in any suitable manner, forexample, by spot welding. The side portions of the anode 24 extend pastthe electron emitting portion of the cathode structure so that the anode24 surrounds three sides of such portion of the cathode structure. Theintermediate portion 50 of the anode is rectangular and is spaced fromthe wires 31 forming the electron emitting portion of the cathode.Electrons from the cathode strike a central target area 51 of suchintermediate portion and such portion is subjected to considerabletemperature and electrical stresses. A portion correspondingapproximately to the target area 51 is therefore preferably displacedout of the general plane of the intermediate portion of the anode 24 byan embossing operation as indicated at 52 in FIG. 4. This providesstiffening portions surrounding the target area of the anode. As shownin FIGS. 1 and 2, the intermediate portion of the anode 24 is preferablyinclined in a direction longitudinally of the wires 31 with respect to anormal to the axis of the tube so that X-rays will be propagated fromthe target area 51 to the right in FIG. 1 from the area 51 shown in FIG.2. A suitable angle of inclination of said intermediate portion relativeto the normal referred to has been found to be 7.

As shown most clearly in FIGS. 1 and 3, the leads 32 for the cathodestructure 30 each have their portions adjacent the wires 31 formed intoa plurality of parallel elements 54, 56 and 58 connected by reversebonds. The parallel elements 54 of the two leads which are farthest fromthe wires 31 are relatively close together. The intermediate parallelelements 56 are farther apart and the parallel elements 58 nearest thewires 31 are still farther apart so as to provide a concave or troug-shaped resultant structure when viewed in end elevation as in FIG. 2.The leads 26 also include end elements 60 extending across the ends ofsuch trough-shaped structure from the ends of the parallel elements 58.The end elements 60 of each lead terminate in an end portion 62 adjacentbut spaced from the reverse bend between the elements 56 and 58 of theother lead 32. Such end portion of each lead extends generally normal tothe parallel elements 56 and 58 of the other lead and in a directiontoward the cathode end of the tube. The end elements 60 are curved sothat their central portions are at a greater distance from theintermediate portion 50 of the anode than their end portions. The smalldiameter wires 31 forming the electron emitting portion of the cathodestructure 30 extend between the end elements 60 and are secured by spotwelding to the surfaces of such end elements which are remote from theintermediate portion 5d of the anode structure.

It will be apparent that heating current flowing through the leads 32will flow in parallel through the wires 31. The wires 31 and leads 32are preferably made of tungsten and in operation of the tube, such wiresare heated by a heating current for a short period of time to atemperature of the order of 2900 to 3000" K. The leads 32 are alsoheated by such current, such that the elements 54, at, 5'3 and 60 of theleads reach a temperature of the order of 1900 to 2000 K. This causesimpurities to be evaporated from the surfaces of such leads as well asfrom the wires 31 and also causes a smoothing action due to migration ofatoms on the heated surfaces. It is apparent that lower work functionmaterials such as thoriated tungsten may be employed for the wires 31 inwhich case the operating temperature of such wires can be lowered andthe relative size of such wires and the leads can be adjusted to stillproduce a self-cleaning and smoothing temperature of the leads. Alsowhile a plurality of filament wires are shown in the cathode structuredisclosed, it is apparent that a single filament wire can be employedetween a pair of leads.

'of such socket.

When a high voltage is impressed between the anode 24 and the cathodestructure 60 so that the anode becomes highly positive relative to thecathode structure, streams of electrons resulting from both thermalemission and field emission flow from the wires 31 to the anode 24. Theelements 54, 56, 58, 60 and 62 of the leads act as a focusing structureto cause substantially all of such electrons to strike the areas 51 ofthe anode 24.

The heating current for the cathode structure is supplied to the leads32 through the larger leads 34 which extend through the seal 35 and intoa recess 64 provided by the reentrant seal structure 36. The leads 34are connected in such recess to connector pins 66 held in position inspaced relation to each other by a spacer element 68 of insulatingmaterial and by having their head portions imbedded in a body 70 ofinsulating material cast in situ in and filling therecess 64. One of thepins 66 also can be employed to provide a cathode connection forapplying voltage pulses between the anode structure 22 and the cathodestructure 30. The element 72 may be a plastic or glass cover for thevacuum seal off tube shown in dotted linesat 74 in FIG. 1.

The leads 26 for the anode structure 22 extend through the pressseal 27into a recess '76 provided by the reentrant seal structure 28 at theanode end of the tube. As shown most clearly in FIG. 10, the exteriorends of leads 26 extend through spaced apertures in a small metalterminal block 7 8 and are held therein by setscrew 80. A third lead 81extends through the seal 27 between the leads 26 and has its endextending through an aperture in another small metal terminal block 82.Such end is held in the aperture in the block 82 by a set screw 84. Thetwo blocks 78 and 82 are insulated from each other by a small strip 86of insulating material. The recess 76 is otherwise filled with abody ofinsulating material 88 except for an axially extending cylindricalsocket 90 formed in the resin. The socket 90 extends from the exteriorsurface of the insulating body-88 to the blocks 78 and 82 so .thatsurfaces of such blocks form the bottom surface The blocks are otherwiseimbedded in the body of insulating material, which material may be casein situ in the recess 76. a

The socket 90 has a diameter providing a snug slidin fit for the end ofthe cylindrical solid dielectric 92 of a conventional coaxial cable fromwhich the outer tubular conductor 94 has been removed. The block 78 isprovided with a tapered aperture 96 concentric with socket 90 for thereception of .a protruding end of the central conductor 98 of thecoaxial cable. The body 88 of insulating material is preferably somewhatflexible and may, for example, be an epoxy resin or a silicone resin.The same types of resins may also be employed for the body 70 ofinsulating material at the cathode end of the tube.

The solid dielectric of the coaxial cable is also somewhat flexible andby merely pushing the stripped end of such cable into the socket 90so-as to force the free end of the central conductor 98 into the hole 96in the block 7 8, an anode connection is provided which is not easilydisplaced and which eifectively blocks any external a-ir path for flashovers between the anode and cathode connections.

The other block 82 partly imbedded in the body 88 of insulating materialprovides a connection for one end of the getter heater 46 when the anodeconnecting cable is removed. The other end of such heater is connectedto an end of the member 44 which in turn is connected to one of theanode lead 26 so that heating current may flow through the heater 46 ina gettering operation performed before the tube is put in operation orafter operation of the tube to recondition it if gas develops therein.

In operation the tube is positioned in a suitable sup port. A lowvoltage, for example, 6.3 volts is impressed across the cathodeconnection pins 66 to produce a heating current through the electronemitting filament wires 31 and the supporting leads 32 therefor. Suchvoltage is maintained for approximately 3 seconds and the wire sizes aresuch that the wires 31 are heated to 2900 to 3000 K. and leads 32adjacent the wires 31 to 1900 to 2000 K. This means that the leadsshould have several times the cross-sectional area of the totalcross-sectional areas of the filament wires, if made of the same metalas the filament wires. It will be apparent that the relative areas willvary if different metals are employed for the leads and filament wires.As a specific example, five tungsten filament wires 31 each 10 mils indiameter and approximately 1%-inches long can be employed. The leads 26may also be of tungsten and have a diameter of approximately 60 mils. Atthe end of a three second heating period a square wave pulse of voltage,for example, a 300 kv. pulse having a length of 0.2 microsecond, isimpressed across the anode and cathode connections of the tube toproduce a current through the tube of approximately 1000 amperes. Suchvoltage is sufficiently high that a large portion of the electronemission from the small diameter filament Wires 31 is field emission andan intense beam of electrons emitted from such wires is focused on thetarget area 50 of the anode by the cathode structure to produce anintense source of X-rays for a very short time. Higher voltage shortertime pulses can be employed and it is apparent that lower voltage pulsesof the same or greater time periods may be employed. If a tube has beenout of operation for a period of several days, two or more operations ofthe tube at lower voltages are advisable to condition the tube forhigher voltage operations.

T he voltage pulses discussed above can be produced, for example, by thedischarge of electrical energy stored in banks of transmission lines,such as lumped constant lines or coaxial cables by charging such linesfrom high voltage sources.

A modified cathode structure 100 is shown in FIGS. 5 to 7. Such cathodestructure is similar to the cathode structure of FIGS. 1, 2 and 3, inthat a plurality of wires 31 of small diameter extend between endelements 102 forming part of the supporting leads 104 for the cathode.The two leads 104 also have reverse bends to provide parallel sideelements 106, 108 and 110 forming part of a focusing structure. Theleads 104 terminate in end portions 112 bent to form a rectangular endstructure with the end element 102. The side elements 106, 108 and 110and end elements 102 in conjunction with the end portions 112 form ahollow rectangular structure in which is positioned a focusing element114 having a surface directed toward the anode of the tube, such as ananode 24 of FIG. 4. The focusing element 114 may be supported on aseparate lead 116 passing through a press seal 118 for the leads 104. Inoperation the lead 116 will be connected to one of the leads 104 throughan external connection. It is apparent that the cathode structure 100 ofFIGS. 5 to 7 may be substituted for the cathode structure 22 in a tubeotherwise similar to that shown in FIG. 1.

A modified anode structure 120 is shown in FIG. 8 and FIG. 811 asincluding an anode 122 of thin metal foil such as tungsten foil .001 to.002 mil thick. Such foil is formed into an elongated semicirculartrough-shaped anode element and is supported at its longitudinal edgesby spring clips 124 of thin sheet metal in turn supported on the ends ofanode leads 126, which ends are bent to properly position the anoderelative to the cathode structure of the tube. The edges of the foilanode 122 are each folded and engaged in a double fold along onelongitudinal edge of one of the clips 124. Such clips also havecylindrical portions along their outer longitudinal edges fitting theends of the leads 126. T he-joint structure just described provideseifective support on and electrical connection of the anode 122 to theleads 126 under widely diiferent temperature conditions even though thespring clips 124 are of a different metal than the anode 122 arr/gees orleads 125 so as to have a different temperature coefficient ofexpansion.

The anode structure 122 of FIGS. 8 and 8a may be substituted for theanode structure 22 of FiGS. 1, 2 and 4, in tubes otherwise similar tothose above described so as to be employed with the cathode structures3% or 1%, also described above. The thin anode 122 provides for X-rayemission from the surface of such anode which is remote from the cathodestructure and also enables the anode to be heated by heating currentsupplied through the leads 126 during out gassing of the tube elements.

The tubes of the present invention are particularly adapted for highspeed X-ray work where it is desired to take X-ray photographs ofrapidly moving objects, but can also be employed for various other typesof X-ray work.

We claim:

1. An X-ray tube comprising an evacuated envelope, an anode supported insaid envelope and having an anode electrical connection extending to theexterior of said envelope, a cathode structure including a pair ofspaced leads supported in said envelope and having electricalconnections extending to the exterior of said envelope in spacedrelation to said anode connection, said leads each providing a cathodesupport portion adjacent said anode, said support portions being spacedfrom each other and from said anode, and a filament wire secured to andextending in a substantially straight line between said supportportions, said leads and filament wire being proportioned to provide forheating said leads adjacent said anode including said support portionsto a surface cleaning and smoothing temperature below a thermal electron emission temperature when a heating current is passed in seriesthrough said leads and filament wire in an amount heating said filamentwires to a thermal electron emission temperature.

2. An X-ray tube comprising an evacuated envelope, an anode and acathode structure supported in said envelope, said cathode structureincluding a pair of spaced leads each providing a cathode supportportion adjacent said anode, said support portions being spaced fromeach other, and a filament wire secured to and extending in asubstantially straight line between said support portions, said leadsand filament wire being proportioned to provide for heating said leadsadjacent said anode including said support portions to a surfacecleaning and smoothing temperature below a thermal electron emissiontemperature when a heating current is passed in series through saidleads and filament wire in an amount heating said filament wires to athermal electron emission temperature.

3. An X-ray tube comprising an evacuated envelope, an anode and acathode structure supported in said envelope, said cathode structureincluding a pair of spaced leads, said leads each providing a cathodesupport portion adjacent said anode, said support portions being spacedfrom each other, and a plurality of spaced substantially parallelfilament wires secured to and extending between said support portionstoprovide a cathode portion of said structure, said leads each having apart extending generally parallel to said filament wires adjacent a sideof said cathode portion to provide focusing portions adjacent said anodefor electron beams from said Wires, said leads and filament wires beingproportioned to provide for heating said leads adjacent said cathodeportion including said support portions to a surface cleaning andsmoothing temperature below a thermal electron emission temperature whena heating current is passed in series through said leads and filamentwires in an amount heating said filament wires to a thermal electronemission temperature.

4. An X-ray tube comprising an evacuated envelope, an anode supported insaid envelope and having an anode electrical connection extending to theexterior of said envelope, a cathode structure including a pair ofspaced leads supported in said envelope and having electricalconnections extending to the exterior of said envelope in spacedrelation to said anode connection, said leads each providing a cathodesupport portion adjacent said anode, said support portions being spacedfrom each other and from said anode, and a plurality of spaced filamentwires secured to and extending between said support portion to provide acathode portion, said leads each having a part extending generallyparallel to said filament wires adjacent a side of said cathode portionto provide focusing portions adjacent said anode to direct electronsemitted from said wires toward said anode when a voltage pulse isimpressed between said anode and said cathode structure, said leads andfilament wires being proportioned to provide for heating said leadsadjacent said anode including said support and focusing portions to asurface cleaning and smoothing temperature below a thermal electronemission temperature when a heating current is passed through said leadsand filament wires in an amount heating said filament wires to a thermalelectron emission temperature.

5. An X-ray tube comprising an evacuated envelope, an anode supported insaid envelope and having a target area and an anode electricalconnection extending to the exterior of said envelope, a cathodestructure including a pair of spaced leads supported in said envelopeand having electrical connections extending to the exterior of saidenvelope in spaced relation to said anode connection, said leadsproviding spaced cathode support portions adjacent said anode andextending generally parallel to each other and to said target area, anda plurality of spaced filament wires secured to and extending betweensaid support portions to provide a cathode portion, said leads eachhaving parts extending generally parallel to said filament wiresadjacent a side of said cathode portion to provide focusing portions todirect electrons emitted from said wires against said target area when avoltage pulse is impressed between said anode and said cathodestructure.

6. An X-ray tube comprising an evacuated envelope, an anode supported insaid envelope and having a target area and an anode electricalconnection extending to the exterior of said envelope, a cathodestructure including a pair of spaced leads supported in said envelopeand having electrical connections extending to the exterior of saidenvelope in spaced relation to said anode connection, said leadsproviding spaced cathode support portions adjacent said anode andextending generally parallel to each other and to said target area, anda plurality of spaced filament Wires secured to nd extending betweensaid support portions to provide a cathode portion, said leads eachhaving a plurality of parts connected to each other by reverse bends andextending generally parallel to said filament Wires adjacent a side ofsaid cathode portion to provide focusing portions to direct electronsemitted from said wires against said target area when a voltage pulse isimpressed between said anode and said cathode structure.

7. An X-ray tube comprising an evacuated envelope, an anode supported insaid envelope and having a target area and an anode electricalconnection extending to the exterior of said envelope, a cathodestructure including a pair of spaced leads supported in said envelopeand having electrical connections extending to the exterior of saidenvelope in spaced relation to said anode connection, said leadsproviding spaced cathode support portions adjacent said anode andextending generally parallel to each other and to said target area, aplurality of spaced filament wires secured to and extending between saidsupport portions to provide a cathode portion, said leads each having aplurality of parts connected to each other by reverse bends andextending generally parallel to said filament wires adjacent a side ofsaid cathode portion to provide focusing portions to direct electronsemitted from said wires against said target area when'a voltage pulse isimpressed between said anode and said cathode structure, said wires andsaid leads including said focusing portions and said support portionsproviding a hollow structure, and a focusing element positioned withinsaid hollow structure and having a surface directed toward said wires toassist in directing said electrons.

8. An X-ray-tube comprising an evacuated envelope, an anode and acathode structure supported in said envelope, said cathode structureincluding a pair of spaced leads providing spaced cathode supportportions adjacent said anode and extending generally parallel to eachother, and a plurality of spaced filament wires secured to and extendingbetween said support portions to provide a cathode portion, said leadseach having parts extending generally parallel to said filament wiresadjacent a side of said'cathode portion and intermediate said supportportions to provide focusing portions for electrons emitted from saidwires.

9. An X-ray tube comprising an evacuated envelope, an anode and acathode structure supported in said envelope, said cathode structureincluding a pair of spaced leads providing spaced cathode supportportions adjacent said anode and extending generally parallel to eachother, a plurality of spaced filament wires secured to and extendingbetween said support portions to provide a cathode portion, said leadseach having parts extending generally parallel to said filament wiresadjacent a side of said cathode portion and intermediate said supportportions to provide focusing portions for electrons emitted from saidwires, said wires and said leads including said focusing portions andsaid support portions providing a hollow structure, and a focusingelement in said hollow structure having a surface directed toward saidwires.

10. An X-ray tube comprising an evacuated envelope, an anode structureincluding a pair of spaced leads supported in said envelope and havingelectrical connections extending to the exterior of said envelope, acathode structure supported in said envelope and having electricalconnections extending to the exterior of said envelope in spacedrelation to said anode connections, said leads providing spaced anodesupport portions extending generally parallel to each other, said anodebeing a trough-shaped element of metal foil having folded longitudinaledges adjacent said support portions, spring clips having foldedportions engaging said folded edges and portions fitting and supportedby said support portions, said anode extending partly around saidcathode structure.

11. An X-ray tube comprising an elongated evacuated envelope, an anodesupported in said envelope and having an anode electrical connectionextending to the exterior of one end of said envelope, a cathodestructure supported in said envelope in spaced relation to said anodeand having electrical connections extending to the exterior of the otherend of said tube, said one end of said envelope having a reentrantportion of insulating material providing a recess, the exterior portionof said anode connection terminating within said recess intermediate thedepth of said recess in a terminal portion, a body of insulatingmaterial filling said recess around said exterior portion and having acylindrical socket therein extending axially of said recess from theopen end of said recess to said terminal portion for receiving andfitting an insulating sheath of a solid dielectric coaxial cable fromwhich the outer tubular conductor of said cable has been removed tothereby provide for engagement of the inner conductor of said cable withsaid terminal portion and for blocking air paths for electrical flashovers around said tube.

12. An X-ray tube comprising an evacuated envelope and electricalconnection structure for said tube, said structure including a reentrantportion of insulating material forming part of said envelope providing arecess, an electrical connection extending through said envelope andhaving an exterior portion terminating within said recess in a terminalportion intermediate the depth of said recess, a body of insulatingmaterial filling said recess around said exterior portion and having acylindrical socket therein extending axially of said recess from theopen end of said recess to said terminal portion for receiving andfitting an insulating sheath of a solid dielectric coaxial cable fromwhich the outer tubular conductor of said cable has been removed tothereby provide for engagement of the inner conductor of said cable withsaid terminal portion and for blocking air paths for electrical flashovers around said tube.

13. An X-ray tube comprising an evacuated envelope, an anode supportedin said envelope and providing an electron receiving surface and havingan electrical connection extending to the exterior of said envelope, acathode structure including a pair of spaced leads supported in saidenvelope and having electrical connections extending to the exterior ofsaid envelope, each of said leads having a support portion spaced fromand extending generally parallel to said surface, said support portionsbeing generally parallel to and spaced from each other, a plurality offilament Wires electrically connected at their ends to said supportportions and extending between said portions in substantially straightlines and in generally parallel relationship to each other and to saidsurface.

References Cited in the file of this patent UNITED STATES PATENTS1,559,715 Lilienfeld Nov. 3, 1925 1,613,503 Daumann Jan. 4, 19271,738,959 Mutscheller Dec. 10, 1929 1,852,020 Metcalf Apr. 5, 19322,110,259 Bouwers Mar. 8, 1938 2,141,933 Perrott Dec. 27, 1938 2,167,275Gross et a1. July 25, 1939 2,202,687 Bouwers May 28, 1940 2,385,380Ratchford Sept. 25, 1945 2,471,298 Atlee May 24, 1949 2,488,716 ElenbaasNov. 22, 1949 2,597,817 Poittevin May 20, 1952 2,720,607 Criscuolo et a1Oct. 11, 1955 2,802,190 Talpey Aug. 6, 1957 2,788,503 Millis Apr. 9,1957 2,886,725 Yanagisawa May 12, 1959 2,896,105 Hosemann July 21, 19592,900,542 McEuen Aug. 18, 1959 2,906,912 Litton Sept. 29, 1959 2,909,664Zunick et al. Oct. 20, 1959 2,922,916 Sharkey Ian. 26, 1960 FOREIGNPATENTS 559,374 Canada June 24, 1958 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No 3, 179 ,832 April 20, 1965 Walter P.Dyke et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6, line 70, for "outer" read other column 8, line 49, for "nd"read and Signed and sealed this 21st day of September 1965.

(SEAL) Altest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF" CORRECTION PatentNo, 5 179 ,832 April 20, 1965 Walter P. Dyke'et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 6, line 70, for "outer" read other column 8, line 49, for "nd"read and Signed and sealed this 21st day of September 1965.v

FQSEAL) Allest:

ERNEST w. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

8. AN X-RAY TUBE COMPRISING AN EVACUATED ENVELOPE, AN ANODE AND ACATHODE STRUCTURE SUPPORTED IN SAID ENVELOPE, SAID CATHODE STRUCTUREINCLUDING A PAIR OF SPACED LEADS PROVIDING SPACED CATHODE SUPPORTPORTIONS ADJACENT SAID ANODE AND EXTENDING GENERALLY PARALLEL TO EACHOTHER, AND A PLURALITY OF SPACED FILAMENT WIRES SECURED TO AND EXTENDINGBETWEEN SAID SUPPORT PORTIONS TO PROVIDE A